1. Field of the Invention
The present invention relates to a beam management method enabling simultaneous beam forming by a multi-functional phased array radar including a plurlity of phased array antennas (PAAs) disposed adjacent from one another in order to search and track targets while avoiding mutual interference between the phased array antennas, and an apparatus therefor.
2. Prior Art
FIG. 1 is a block diagram showing a beam management method of the prior art (See, for example, W. A. Mulle, "A radar/phased array radar primer" in RCA Engineer 31-5, September/October/November 1986, pages 68-76). In a step 102 of the managing method, various parameters of the targets being tracked by the respective PAAs are temporarily stored. In a step 104, the positions of searching beams are calculated, and in a step 106, timings of transmission of searching beams are assigned to the respective PAAs so as to ensure predetermined periods of search time. In a step 108, timings to radiate tracking beams are assigned to the respective PAAs on the basis of the stored parameters of the targets. In order that the timings of the searching beams do not overlap those of the tracking beams, and that the searching or tracking operation performed by the same PAA are not repeated, scheduling is conducted for a PAA.sub.j (1.ltoreq.j.ltoreq.N) in a step 110. A beam scan calculator (BSC) is driven for the PAA.sub.j to provide the PAA.sub.j with a necessary amount of phase shift to cause a beam to be formed in a step 112. Then a comparison is made between j and N in a step 114. If j is smaller than N, after an echo is received, the value of j is incremented by one in a step 116 (j=i+1). Similar procedures are taken until j becomes equal to N, and the procedure returned to the step 106.
Such timings for searching and tracking operations are time-division-multiplexed, as shown in FIG. 2. For example, the PAA 1 is operated in the search mode followed by the tracking operations by PAAs 1-4 in this order. Next, the PAA 2 is operated in the search mode and tracking operations by the PAAs 1-4 then follow in this order, and so on.
FIG. 3 is a block diagram showing the construction of a phased array radar system of the prior art, as described in the above-identified article by Mulle. Phased array radars generally have a plurality of PAAs, and this figure shows, the most common number, four, PAAs. In FIG. 3, the prior art system comprises four PAAs 120, 122, 124 and 126 each conducting searching and tracking operations in different one-quarter portions of a hemispherical range, and an antenna selector 128 for selecting one of the four PAAs. A TR switch 130 follows the antenna selector 128 to switch between a transmitter 132 and a receiver 134.
A tracking computer 136 is connected to the receiver 134 for tracking a target on the basis of a signal received from the receiver and calculating target parameters. A searching beam position computer 140 is provided for calculating a searching beam position. A BSC 142 operates to calculate amounts of phase shift to be set to the PAAs 120-126. A scheduler 144 is positioned between the BSC and the tracking computer 136 and the searching beam position computer 140 for allotting beam radiating timings of searching and target tracking operations to the PAAs and driving the BSC in accordance with the calculated timings.
In such a radar system, the respective PAAs radiate beams in a time-division-multiplexing manner as shown in FIG. 2.
It is essentially necessary to avoid any mutual interference between a plurality of PAAs closely disposed to each other. To do this, it is advisable to employ what is called a "synchronization system" wherein all the PAAs repeatedly transmit, at the same time, pulses having the same pulse width at the same pulse repetition rate (hereinafter called "PRT") so that the transmission by one PAA does not overlap the reception by another PAA.
As for target tracking, however, because a range, a desired clutter suppression ratio and so on are different for each target, the width of transmitted pulses and the PRTs have to be different. (There are, for example, long, medium and short PRTs.) Consequently, it is impossible to employ the synchronization system.
As a result, in the prior art radar system, the searching and tracking beams have to be radiated from the respective PAAs in such a time-division-multiplexed manner as shown in FIG. 2. This causes a significant amount of time to be taken to complete the searching operations, to detect targets in a predetermined area. Conversely, if a short period of time is present for searching targets in a predetermined area, the number of targets to be tracked is significantly reduced.